Vergara - 1976 - Physiological and morphological adaptability of ri

404 CLIMATE AND RICE
Disease onset was accomplished by artificial inoculations with the same
isolate of race T of H. majvdis used in the controlled environment studies. Disease
onset was simulated to have occurred by single- and multiple-focus introduction
of primary inoculum. In 1971. the simulated single-focus infection was accomplished
by inoculating a small cluster of plants in the center of the plot. In 1972
and 1973. single-focus plots were inoculated in the upward corner of the plots
to enable us to compare disease increase by using time and disease dispersal
gradients as prime factors. Multiple-focus infections tvere accomplished by
inoculating 200 plants evenly spaced throughout the plots. Plants were inoculated
by placing sections of diseased leaves in the whorl of plants.
Prior to disease onset, two areas on the midrib of the 3rd, 5th, 7th. 9th. and
llth leaves of 600 evenly spaced plants were marked with an indelible pen. A
5.08 >< 5.08 cm area was cut out of a slightly larger piece of cardboard and a
permanent mark was placed on the cardboard in the middle of the loiver side of
the square. Twice weekly beginning in late July. field workers monitored disease
by placing the marked area of the cardboard device on the marked area of the
midrib and counting the number of lesions within the 5.08 >< 5.08 cm leaf area.
I.ater in the season. when lesion coalescence made counting difficult on the
lower leaves, lesion area on the third and fifth leaves was estimated as a percent
of total area within the square and the number of lesions calculated by multiplying
percent diseased tissue by a constant value of 40. This was done since
4O lesions each approximately 6O mm= in size would fully occupy the monitored
area on those leaves. Progressively higher constant values were assigned to the
seventh, ninth. and eleventh leaves since average lesion size decreases on the
higher leaves. Values ofx and r sensu van der Plank (I963) were calculated for
each monitoring time from the 6.000 pieces of data obtained from the 10 areas
on 600 plants.
Environmental data were recorded hourly throughout the monitoring period
Temperature was measured using copper-constantan thermocouples. Relative
humidity (RH) was measured with a Phys-Chemical Research Corporation
PCRC-SS mini electronic humidity sensor. Wind speed was monitored with a
Hastings-Raydist type N-7B hot wire anemometer. Rainfall was measured with
a standard 8-inch, weighing-type rain gauge converted to record electronically’.
All sensors ‘were connected to a Heivlett-Paekard R-2OI7D Data Acquisition
Unit which recorded the data on tapes for computer use. Temperature, RI l. and
“find speed were measured at heights of 0.5, l. 2. 4. and 6 meters above the
ground located near the center of the field plot.
Kramer-Collins spore traps were utilized to obtain a measure of H. mqvdis
spores present in the air throughout the season. Traps were located at l and 2m
heights within the plot. The traps were programmed to sample four 5-minute
periods per hour, 24 hours a day. Each day the slides were removed from the
traps and the number of H. mcrvdis spores trapped per hour were counted. In
1973, glass rods xvere used also to trap spores and the relative efficiency of the
two methods was compared.